Actor Robert Pattinson says he does not know how to act.

"I don't really know how to act, I kind of wanted to somehow make it real, and one of the ways I've always thought makes that a little bit easier is if you shake up your physical state just before action. You end up walking into a scene having a different ... feeling," Pattinson told the Observer newspaper, reports femalefirst.co.uk.

At times, the 33-year-old star would gag so hard that he'd actually throw up.

"I forgot I had a mic on the whole time, so the producers and the director, before every single take of the movie, would get ... It kind of puts everyone else off," he said.

The London-born actor admits to being a "catastrophist".

However, Pattinson feels that in some instances, his pessimistic outlook can be beneficial.

"I'm a catastrophist. I'm always thinking that the worst-case scenario is actually going to happen. So when it does happen, I'm like: 'Gah! OK! I'm prepared!'"

He also shared that he's drawn to particular types of on-screen characters.

Pattinson said: "I'm not entirely sure how to play, like, a normal person. I don't think I'm great at subtle.I like characters who, when a situation is placed upon them, their decision-making process is incomprehensible.

The actor says he finds it fascinating when people make bad decisions.

"The humour and the befuddlement," he added.